This invention relates to circuit interrupters, and more particularly, to a circuit interrupter rotary contact arm assemblies for circuit breakers.
Contact pairs are commonly arranged upon one movable rotary contact arm, such as described within U.S. Pat. No. 4,910,485 entitled xe2x80x9cMULTIPLE CIRCUIT BREAKER WITH DOUBLE BREAK ROTARY CONTACTxe2x80x9d. When an overcurrent condition exists, electromagnetic forces cause the rotary contact arm to separate from fixed contacts against the closing force of one or more contact springs.
The rotary contact arm is typically connected to the contact springs via pivotal links. During quiescent operation, the contact springs provide a force to the rotary contact arm via the links in a direction as to drive the rotary contact arm into the fixed contacts. Upon short circuit condition, for example, current levels at or above the xe2x80x9cwithstand levelxe2x80x9d of the interrupter, the electromagnetic forces generated between the fixed contacts and the rotary contact arm causes the rotary contact arm to rotate away from the fixed contacts. If the overcurrent level reaches or exceeds the xe2x80x9clet-through levelxe2x80x9d, the spring force passes a point commonly referred to as the xe2x80x9covercenterxe2x80x9d position and the rotational direction of the contact spring force changes, i.e., the contact springs provide a force to the rotary contact arm via the links in a direction as to drive the rotary contact arm apart from the fixed contacts.
It is desirable to allow the rotary contact arm to pop open and reclose at low short circuit levels, e.g., below the let-through level.
Additionally, it is desirable to allow the rotary contact arm to open and remain locked open at high short circuit levels.
A circuit interrupting mechanism comprises a first and second electrical conductor and a movable contact arm positioned between said first and second electrical conductor. The contact arm rotates about a central pivot and includes an upper link pivotally attached at an upper link pivot point on the contact arm and a lower link pivotally attached at a lower link pivot point on on the contact arm.
The contact arm is configured, positioned and dimensioned for rotational movement about said central pivot between a first position and a second position. The first position electrically connects said first electrical conductor to said second electrical conductor. The second position prohibits an electrical connection between said first electrical conductor and said second electrical conductor;
The circuit interrupter mechanism further includes a spring positioned to provide a force to the contact arm. A first pin and a second pin are positioned relative to a first end and a second end of the spring. The upper link has an upper link receiving area and the lower link has a lower link receiving area. The first pin is in the upper link receiving area and the second pin is in the lower link receiving area.
An overcenter position of the contact arm is defined between the first position and the second position. The overcenter position is the rotational position where the first pin, the upper link pivot point, the central pivot, the lower link pivot point and the second pin are aligned.
The spring exerts a force urging the first pin toward the upper link receiving area and an opposite force urging the second pin toward said first lower link receiving area. The opposing forces force creating a contact arm torque about said central pivot toward the first position when the contact arm is between the first position and the overcenter position. The contact arm torque reverses past the overcenter position such that the torque is toward the second position when the contact arm is between the overcenter position and the second position.